Resistor unit and method of forming same



Dec. 8, 1931. BRADLEY 1,835,267

RESISTOR UNIT AND METHOD OF FORMING SAME @Mw/sow Lymj E Emma/ Dec. 8, 1931. L BRADLEY 1,835,267

RESISTOR UNIT AND METHOD OF FORMING SAME Filed Aug. 3l, 1925 2 Sheets-Sheet 2 Patented Dec. 8, 1931 UNITED STATES PATENT OFFICE LYNDE BRADLEY, OF MILWAUKEE, WISCONSIN, ASSIGNOR, BY MESNE IASSIGNMENTS,

OF ONE-HALF TO HIMSELF AND ONE-HALF T0 HARRY L. BRADLEY, BOTH OF MIL- WAUKEE, WISCONSIN BESISTOR UNIT AND METHOD 0F FORMING SAME Application med August 31, 1925. Serial No. 53,570.

This invention has as one of its objects the .provision of an improved resistor unit of a type especially adapted for use in radio receiving and broadcasting apparatus, but capable of utilization in any other situation requiring a resistor unit.

Another object of this invention resides in the provision of an improved resistor unit of the fixed type and method of producing the same, the principles of which may he employed in the production of resistor units designed for use in compressible resistor elements, as described in m co-pending application, Serial No. 517 23, led August 19, 199.5

.' of which this is a continuance in part.

Many attempts have been made, particularly in recent years as a result of the development ot' the radio art, to produce fixed resistor units capable of efiicient use in connection with radio broadcasting and receiving, but without any preceptible degree of success by reason of the fact that, heretofore, it has been impossible to calibrate the resistance value of a unit, as a result of which no two units manufactured at the same time and under the same conditions had the same resistance value or conductive characteristics.

Having this objectionable feature in mind, it is an object of my invention to provide an improved method of and apparatus for forming resistor units whereby their resistance value may be adjusted to approximately any desired degree, which value they maintain without change.

Another' object of this invention resides in the provision of an improved method of forming resistor units wherein the units are subjected to the infiuence of an electrical current having the power to so change the characteristics of the units as to increase their conductivcncss whereby the resistance value of the units may/be calibrated by subjecting the same to the influence of the current until their' value reaches a desired point.

Another object of this invention resides in the provision of an improved type of fixed resistor unit which is so designed as to be capable of convenient connection within an electrical circuit by bein either removably secured between two spring contacts or by having the ends of a bus line soldered in sockets formed on the ends of the unit.

It .is a further object of my invention to provide an improved resistor unit having provlsion for facilitating its connection in a bus wire or conductor so that the heat incidental to the soldering action in no wise damages the unit.

Still a further object ofthis invention ree sides in the provision of an improved method of forming resistor units of the character described in an economical and practical manner so as to avoid subjecting the umts to internal strains or stresses and thus prevent the changing of their conductive resistance after having been once calibrated.

With the above and other objects in View which will appear as the description proceeds, my invention resides in the novel method, construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that sach changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.-v

In the accompanying drawings, l have illustrated several complete examples of the physical embodiment of my invention constructed accordingto the best modes I have so far devised for the practical application off the principles thereof, and in which:

Figure 1 is a view, partly in section and partly in elevation, of a mold for forming.

my improved type of resistor unit;

Figure 2 is a View similar to Figure 1 illustrating the manner of maintaining the units in the mold against expansion while being subjected to heat;

Figure 3 is a perspective view, with parts broken away, of the manner of packing the units in a receptacle prior to subjection to a second heat treatment;

Figure 4 is a diagrammatic View of the electrical circuits and mechanism for adjusting the resistance value of a unit;

Figure 5 is a view, partly in section and partly in elevation, illustrating one form of completed resistor unit;

Figure 6 is a view similar to Figure 2 of a slightly modified type of mold especially adapted for forming a single unit at a time; Figure 7 is a View, partly in section and partly in elevation, o a slightly modified type of resistor unit of the character formed in the mold illustrated in Figure 6;

Figure 8 is a view, partly in section and partly in elevation, illustrating one manner of connecting two units of the construction illustrated in Figure 7 in line, and

Figure 9 is a view similar to Figure 8 illustrating still another manner of securing two of the resistor units end to end.

As illustrated in Figure 5, each unit 5 consists of end terminal members 6 connected by a body of molded material 6 having as its base an organic substance such as a phenol condensation product and graphite. In my co-pending application Serial No. 51,723 of which this is a continuation in part, the composition and manner of mixing the material 6' is described in detail and reference may be had thereto. Y

The end terminal members are preferably of brass or any other good conductor and have their inner ends counterbored or recessed, as at 7, and provided with a central anchoring stud 8, the exterior of which is formed with a series of grooves or recesses 9 into which the material 6" is pressed in molding. The bored end of each terminal member is of a diameter equal to that of the finished unit and its outer end is cone-shaped or tapered, as at 10, to facilitate its mounting between the conventional type of spring clips.

As it is often desirable to embody a unit directly in a bus wire, a socket 11 is formed on the tip or outer end of each terminal member and is filled with solder 13 at the factory so that the user need but apply a flux to the bus wire end and heat the socket by means of a torch or iron and then insert the end of the wire into the solder when the same reaches the molten state. The point of connection between the socket 11 and the terminal member end 10 is very small, as at 12, to protect the unit against excessive heat while soldering a bus wire therein and also to provide means facilitating the cutting off of the socket in the event it is desired to secure the unit between the conventional spring mountings, not shown.

In Figures 1 and 2, the mold illustrated is 5 of the type especially designed for the production of the unit illustrated in Figure 5 and is adapted to form five units at a single operation. The mold proper comprises a cylindrical member 14 havmg five, spaced, parallel bores or openings 15 extending longitudinally therethrough and of a diameter equal .to that of the finished unit and a central bore or opening 16 for the purpose later described. In operation, an end plug member 17 is placed ineach bore 15 and the inner end 18 of each plug is shaped to receive and conform with the terminal member which is positioned in the bore with recessed portion upwards. The proper amount of material 6 is then placed ineaoh bore 15 and terminal members 6 are engaged therein with their recessed portions inwardly and compression plungers 19 inserted in the bores from the top, the inner ends 20 of the compression plungers being shaped similar to the inner ends 18 of the plugs 17.

The bottom plugs 17 are preferably allowed to project a short distance from the member 14 and the mold is positioned on a plate, not shown, having means for accommodating the extended ends of the plugs. The mold and late, not shown, are then positioned on the ed 21 of a hydraulic or other type press and a ring or collar 22 placed on the upper end of the member 14 to limit the movement of the compression members 19 into the bores 15 by the press plunger 23. After the members 19 have been moved into the bores 17 their full limits, the plate,not shown,on which the member 14 rests is removed and the plunger 23 again brought into engagement with the collar 22 to move the plugs 17 into the bores 15 as illustrated in Figure 1. In practice, the pressure a plied by the plunger 23 has been approximately ten tons, although this may be varied.

The mold is moved from the press and the expansion of the units prevented by plates 24 and 25 engaging the ends of the plugs 17 and compression members 19 and held in place by a bolt 26 passed through the central opening or bore 16. The mold is then subjected to a temperature of approximately four hundred degrees Fahrenheit for a period of about one hour, the end plates 24 and 25 holding the units against expansion, as will be readily apparent. The molds are then allowed to cool and the bolt 26 and plates 24 and 25 removed and the units withdrawn by driving the members 19 therethrough. The graphite within the units besides providing the conducting material also lubricates the mold.

The units 5, upon their withdrawal from the mold, are complete in form and are next cured by having their temperature gradually raised to approximately four hundred degrees Fahrenheit and then gradually reduced to approximately room temperature. In actual practice, the gradual control of this heat treatment has been accomplished by burying a carton 27 containing a number of the units in sand or other material in a suitable receptacle 28. It has also been found practical to bury the units directly in the sand, altho the carton 27 ,provides a convenient manner of handling the units.

The receptacle 28 is then placed in an oven maintained at a temperature of approximately two hundred and seventy degrees Fahrenheit for about thirty-six hours. At the end of thirty-six hours, the oven temperature is increased to approximately four hundred degrees Fahrenheit and there maintained for a period of from about seven to eight hours. The receptacle is withdrawn from the oven at the end of the heating period and allowedto cool at room temperature until the units reach a corresponding degree, which requires approximately twelve to fifteen hours. The sand 28 protects the units against sudden increases and decreases in temperature and thus prevents the occurrence of internal strains or stresses that are apt to let go and produce changes in the conductive value of the units after they have been placed in use. The units are next subjected to an electroplating operation to silver plate the contact members 6, the body proper of the unit being composed primarily of a. phenol condensation compound does not accumulate any of the silver deposits from the electroplating bath.

Each unit at this state is complete with the exception that their respective resistance values vary and they are then subjected to the iniiuence of an electrical current having the power to change their conductive characteristics so ,as'to decrease their internal resistance. It is desirable that the internal re sistance of each unit be adjusted to a desired degree according to the use to which the unit is to be put.

In Figure 4 I have illustrated one manner of shooting a unit to adjust the same, in which a pair of spaced contacts 29 and 30 mounted on a. panel 31 are connected with the switch blades 32 and 33 of a control switch 34 by conductors 35 and 36, respectively. The switch 34 is preferably ofthe two pole, double throw type and its stationary contacts 37 and 38 are connected with the shooting circuit 39, to be later described, and its stationary contacts 40 and 41 are connected with the testing circuit 42.

The shooting circuit 39, in the present embodiment, comprises a` spark coil-43, the prima-ry coil 44 of which has one end connected with one side of a battery or other source of energy 45 by a conductor 4G and its other end connected with the vibrator 47 of the coil and with the other side of the battery by a conductor 48, a control switch 49 of conventional type being included in the conductor 48. The secondary coil 50 of the spark coil has one end connected with the stationary contact 37 by a conductor 51 and its other end connected with the contact 52 of an adjustable spark gap device 53 by a conductor 54, the other contact 55 of the device 53 being connected with the contact 38 by a conductor 56, the contact 55 being adjustable with relation to the contact 52 by means of its threaded stud 57.

The testing circuit 42 consists of a source of energy 58, one side of which is connected with the contact 40 by a conductor 59 and its other side with the contact 41 by a conductor 60, a volt meter 61 being interposed in thc conductor 60.

The unit to be tested is engaged between the contacts 29 and 30 to electrically bridge the same and the movable member of switch 34 is swung to engage its contact blades 32 and 33 with the contacts 4() and 41. This action completes the testing circuit and the volt meter indicates the resistance value of the unit. Should the resistance value of the unit be of the desired degree, the switch is opened and the unit removed from the contacts 29 and 30. Experience has demonstrated it to be desirable to so control the ingredients forming the body of the unit that its value will be higher than the desired degree to necessitate its shooting Assuming the unit resistance value is higher" than the desired degree, the switch movable member is swung from the contacts 40 and 41 into electrical connection with the contacts 37 and 38, as a result of which the unit is subjected to the influence of the shooting circuit 39 which has the vpower to so change the characteristics of the unit as to decrease its resistance value. The type of current necessary to accomplish this result may be an oscillating current, or a current having a high frequency or a high potential or any other type of current which will function in the desired manner. After the unit has been shot the movable member is again swung to connect the unit with the testing circuit and a reading taken. If the resistance value of the unit is still high, it is shot again, this process being followed until the value of the unit is brought to within the desired degree.

It has been found from experience that if the resistance value of a unit is unusually high, or if it is stubborn to attempts to decrease its value, a lengthening of the spark gap between the contacts 52 and 55 will more quickly produce a reduction in its resistance value. The unit after having been adjusted to the desired degree as described is complete and will maintain its value without change.

In Figure 6, a slightly modified type of mold is illustrated in which but a single unit is formed at a time, the unit being slightly larger in size than the unit previously described and having a diierent type of end terminal which is preferably in the form of an end plate 62 having either a boss 63 on its outer face or a centrally threaded opening 64 as illustrated in Figure' 8. The inner sides of the terminals 62 have irregular projections 64 thereon similar to the studs 8 to insure their firm embodiment in the completed units.

The mold for forming this type of unit comprises a cylinder 65 having a central opening or bore 66 of a diameter equal t0 that of the finished unit in which an end plug member 67 is inserted and an end terminal 62 placed thereon. The bore is then filled with a desired amount of the` mixed ingredients and an end terminal 62 placed thereon and a compression plunger 68 inserted into the upper end ofthe bore. A cap 69 is next placed over the upper end of the mold which has a central bore 70 to receive the plunger 68 and the outer end` of bore 70 is counterbored, as at 71, to receive the top portion of the cylinder 65, the shoulder 72 formed by the counter-bore limiting the movement of the plunger 68 into the mold, as will be readily apparent. A cap 73 is engaged over the bottom of the mold and when the same has been subjected to full compression by any suitable means, slots 7 4 and 75 in the cylinder and caps, respectively, register, and locking keys 76 are passed therethrough to retain the unit under pressure while being subjected to the initial heat treatment previously described in connection with the unit 5. As the operation of completing the unit is identical with that previously described, further description thereof is deemed unnecessary.

In Figure 7 is illustrated one manner of providing for the connection of the unit Within a circ-uit in which a terminal cap 77 is engaged over each end and secured in place by soldering over the end tip 63 thereof which aligns with an opening 78 in the cap. This type of unit is especially designed for use in connection with a mounting having pairs of spring contacts 79.

In Figures 8 and 9 two units are connected in series to permit the use of either one or both units. In Figure 8 the units are connected by a stud 80 threaded in the adjacent bores 64, a terminal lug 81 being confined between the ends 62 and terminal plates 82 being secured to the outer ends of the units by screws or other means 83 threaded into the bores 64. In Figure 9, the units are secured end to end by a sleeve 84 placed thereover prior to the connection of the units and held in place by solder 85. Caps 77 are then secured over the outer ends of the units. This construction 4facilitates the use of a plurality of units to permit the use of one or two units with a clip type of mounting.

From the foregoing description taken in connection withthe accompanying drawings,

it will be readily obvious to those skilled in the art to which an invention of this character appertains that I provide a very novel and improved resistor unit of the fixed resistance type and a method of and apparatus 70 for forming the same.

I claim:

1. An electrical resistor unit comprising a molded body of materials having the desired conductive characteristics, a terminal mem- 75 ber having one end portion secured to the body, and a-socket on the opposite end of the termmal member for receiving a bus line, the point of connection between the socket and the terminal member per se being small' to 8g thermally isolate the socket from the terminal member and thereby protect the unit from heat incidental to soldering of a bus line in the socket.

2. In an electrical resistor unit a terminal cap mounted on one end of the unit and receiving support therefrom, said terminal cap being taperingly reduced at its outer end to form subtsantially a conical tip, and a socket connected with the tip to receive a bus line, the point of connection between the socket and the conical tip being small in cross sectional area to isolate the socket from the terminal cap and protect the unit against heat incidental to soldering a bus line in the socket.

3. In the method of forming a resistance element, the steps which comprise, compressing a composition of ingredients including phenol condensation product and graphite in predetermined proportions to the desired shapeof the element, subjecting the element to a heat treatment, and subjecting the element to the influence of an oscillatory electric current having the power to increase the conductive characteristics of the element.

4. In the method of forming a resistance element, the steps which comprise, compressing in a mold a composition of ingredients including phenol condensation product and graphite in proportions to produce units of predetermined specific resistance, to a predetermined size and shape, maintaining the element under pressure and subjecting the same to approximately four hundred degrees Fahrenheit for a period of about one hour, permitting the mold to cool and removing the element therefrom, burying the element in a material having the capacity to absorb heat, placing the buried element in an oven having a temperature of approximately two hundred and seventy degrees Fahrenheit, maintaining the oven at that temperature for approximately thirty-six hours, raising the temperature of the oven to approximately four hundred degrees Fahrenheit and maintaining the element at that temperature for approximately twelve to fifteen hours, and gradually permitting the element to cool.

5. The hereindescribed method of forming fixed electrical resistor units which comprises, mixing comminuted conducting and non-conducting materialscomprising a phenol condensation product in proportions to produce units having a specific resistance of a predetermined or greater value, compressling quantities of the mixed materials into solid units of the desired size and sha e, heat curing the units, testing the units or resistance, and subjecting those units having a. specific resistance in excess of said predetermined value to the influence of an oscillatory electric current to reduce their specific resistance. v

6. The hereindescribed method of forming a fixed electrical resistor unit which comprises, mixing` comminuted non-conducting and conducting materials comprising a phe-l nol condensation product in proportions to form units having approximately a predetermined resistance value, placing a quantity of the mixed material in a mold, subjecting the material in the mold to great pressure to solidify the same into a unit of the desired size and shape, and subjecting the unit to an oscillatory electric current to reduce its specific resistance to a predetermined value.

7. The hereindescribed method of forming fixed electrical resistor units which comprises placing a quantity of a composition of comminuted ingredients including a phenol condensation product and graphite in proportions to form units having approximately a. predetermined resistance value, in a mold, subjecting the material in the mold to a great pressure to solidify the same into a unit of the desired size and shape, heat curing the unit, and subjecting the unit to oscillatory electric current to reduce its resistance to a predetermined value.

8. The hereindcscribed method of forming fixed electrical resistor units which comand solidify the material therebetween into a unit of the desired size and shape with the terminal members fixed to its ends, heat treating the unit, maintaining the unit under pressure during the heat treatment to prevent increase in size due to expansion, removing the pressure from the unit, and subjecting the unit to an oscillatory electric current to reduce its resistance to a predetermined value.

In testimony whereof I affix my signature.

LYNDE BRADLEY.

9. The hereindescribed method of forming fixed electrical resistor units which comprises mixing comminuted ingredients including a phenol condensation product and graphite in proportions to produce units having approximately a predetermined resistance value, placing a quantity of the mixed materials in a mold between end terminal members, applying pressure to the terminal members t o force the same together 

